Bolt lock and retracting mechanism for gas operated machine gun



S. M COLL BOLT LOCK RETRACTING MECHANISM 'FOR GAS OPERATED MACHINE GUN Filed NOV. 1952 April 23, 1957 ZiZZ/ MJY Away 9 L ww 4 W.- w Wm -M /4 ah 6 5 \WW/ W/ Unite rates BOLT LOCK AND RETRACTING MECHANISM FOR GAS OPERATED MACHINE GUN Alexander Stone McColl, Kalamazoo, Mich.

Application November 8, 1952, Serial No. 319,554

3 Claims. (Cl. 89-491) This invention relates to improvements in bolt lock and retracting mechanism for gas operated machine gun.

The principal objects of this invention are:

First, to provide a bolt locking and unlocking mechanism and bolt retracting mechanism for a gas operated machine gun in which the bolt is positively locked during firing of the gun and in which the bolt is fully unlocked prior to any bolt retracting force being applied thereto.

Second, to provide a bolt lock that is moved pivotally out of locking engagement with the bolt by the same gas operated element that functions to retract the bolt, the retracting element first acting to unlock the bolt and then proceeding in its motion to impart retracting motion to the bolt.

Third, to provide a bolt locking and retracting mechanism for a machine gun which is relatively simple and inexpensive to manufacture and assemble while at the same time being sturdy in its action.

Fourth, to provide a bolt locking and retracting mechanism for a machine gun that is easily disassembled.

Other objects and advantages of the invention will be apparent from a consideration of the following description and claims.

The drawings of which there are one sheet illustrate a highly practical form of the bolt locking and retracting mechanism.

Fig. 1 is a fragmentary side elevational view of a machine gun embodying the invention.

Fig. 2 is an enlarged fragmentary longitudinal cross sectional view through the gun illustrating the operating parts of the locking and retracting mechanism.

Fig. 3 is an enlarged fragmentary horizontal cross sectional view taken along the plane of the line 33 in Fig. 2.

Fig. 4 is a transverse cross sectional View taken along the plane of the line 44 in Fig. 2.

Fig. 5 is a fragmentary transverse cross sectional view taken along the plane of the line 5-5 in Fig. 3. Generally the gun includes a relatively fixed body or receiver 1 having a cylindrical extension 2 on its forward end which receives the rear end of the barrel 3. The bottom of the receiver is provided with an ear 4 or other suitable structure for mounting the gun on a support and a grip or handle 5 is attached to the rear end of the receiver. The trigger for operating the gun is indicated at 6. Midway along the length of the barrel 3 there is provided a collar 7 that depends below the barrel and has a gas passage 8 formed therein opening between the barrel and the forward end of a gas cylinder 9. The gas cylinder 9 houses a piston 10 having a piston rod 11 extending rearwardly into the front end of the receiver. The rear end of the gas cylinder 9 is threaded into the front end of the receiver as at 12 and a bushing 13 serves as a support and guide for the piston rod.

formed in the bottom wall of the receiver. The rear Patented Apr. 23, 1957 The receiver It is generally rectangular in cross section and is desirably open at the top. A cover 14 is hinged to the top of the receiver as at 15 to close the action chamber formed within the receiver. A releasable catch 16 holds the rear end of the cover in closed position. The mechanism associated with the trigger and the cocking of the necessary firing pin is not important to the present invention and so is not illustrated. It will serve the purpose of the present description to point out that the interior of the receiver is machined to provide a longitudinal slide way 17 for the bolt 18. The rear end of the bolt as illustrated is rectangular in cross section and is retained and guided within the receiver by a guide slot or groove 19 milled in the under side of the cover 14. A slot or opening it} is provided in the side of the gun to receive the ammunition belt. A similar slot not illustrated on the opposite side of the receiver serves as an exit for the expended cartridges and the belt.

Considering the lock mechanism in greater detail it is pointed out that the rear end of the barrel 3 is threaded into the receiver extension 2 as at 21 so that the rear end of the barrel is registered with a hole or port 22 through the front wall of the receiver. The forward end of the bolt 18 is provided with a cylindrical extension 23 that is extended against the inner face of the front wall of the receiver when the bolt is closed. A cylindrical head portion 24 on the extreme forward end of the bolt extension projects into the port 22 to back up the cartridge 25 positioned in the rear end of the barrel. Desirably the head portion 24- is provided with extractor fingers 26 adapted to extract the spent cartridge case from the barrel.

Projecting iaterally from opposite sides of the head portion 2?. are two lu s or ears 27. The port or hole 22 through the front Wall of the receiver is notched as at 23 to accommodate these lugs as they are moved forwardly with the bolt and the generally cylindrical breech portion 22. The rear faces of the lugs 27 terminate generally in the plane of the inner face of the front wall of the receiver although this exact location is not critical to the invention.

The bolt way forming portion 17 at the sides of the receiver is extended forwardly of the forward position of the bolt in two shelflike supports 29 that are positioned alongside of and somewhat below the cylindrical extension 23 of the bolt in the forward position of the bolt. The shelves 29 serve as supports for two locking levers 30 that are vertically supported on the shelves and pivotally connected thereto by pivot pins ill. The forward ends of the levers 3t) carry transversely extending movable keepers 32 that are adapted to coact with the rear faces of the lugs 2'7 to lock the bolt in forward closed position. In order to absorb part of the rearward thrust of the explosion of the cartridge the locking keepers 32 are extended transversely in arcuate wings 33 that project through slots 34 provided therefor in the side walls of the receiver. Springs 35 function to bias the levers 30 and keepers 3-2 inwardly of the receiver into locking engagement with the lugs 27.

Rearwardly from the wings 33 each lever 30 is provided with a depending finger 36 that projects downwardly within the receiver. The fingers 36 are spaced from each other transversely of the receiver and on opposite sides of the center line of the gas cylinder 9 and the piston rod 11. The rear end of the piston rod 11 carries a cam member 37 that slides along the bottom of the receiver and is guided in its motion by a groove 38 face of the cam member 37 is provided with oppositely and rearwardly facing cam surfaces 39 that are adapted to cammingly engage the fingers 36 and spread the fingers apart upon retracting motion of the piston and the cam member 37. Obviously lateral swinging motion of the fingers 36 functions to swing the levers 30 land keepers 32 transversely outwardly and away from locking engagement with the lugs 27.

Depending from the cylindrical front extension 23 of the bolt is a third finger 40 that is positioned behind the fingers 36 in the forward position of the bolt. T he finger 40 which is secured to the bolt is positioned centrally of the receiver where it is engaged by a central flat surface 41 on the cam member 37 after the cam member has spread the fingers 36 and unlocked the bolt. Thus retraction of the piston 10 and cam member 37 functions to first unlock the bolt and to subsequently and positively retract the bolt by expansion of the gases in the gas cylinder 9. It is pointed out that the forward ends of the supporting shelves 29 are terminated at 42 short of the fingers 36 thus permitting lateral swinging motion of the fingers. It is further pointed that the levers 30 extend vertically above the level of the bottoms of the lugs 27 so that as the bolt is retracted the ends of the lugs 27 engage the inner sides of the levers 30 to hold the levers and their connected fingers 36 in laterally spread position. This permits the cam 37 to continue its retracting motion to retract the bolt and to then return to forward position without interfering with the fingers 36. A spring 43 is provided for returning the piston and piston rod and a bolt return spring is indicated at 44 in Fig. 1. A suitable firing pin associated with the bolt is indicated at 45.

It is pointed out that the cam 37 does not necessarily have to retract the full distance through which the bolt is retracted :as the impact and movement of the cam associated with the finger 40 will impart sufficient inertia to the bolt to assure complete retraction of the bolt. A pin 46 having a hand knob 47 on its lower end extends through a slot 48 in the bottom of the receiver and is connected to the cam 37 for manual operation of the bolt.

All of the elements of the bolt locking and retracting mechanism are relatively simple and easy to machine and can be easily assembled through the open top of the receiver. The bolt is positively locked in place during the firing of the gun and no retracting motion can be imparted to the bolt until the keepers have been retracted to unlock the bolt. The action is thus smooth in operation and well adapted to perform its designed function. Obviously various modifications and details of the action can be made without departing from the spirit of the invention as defined in the claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. A gas operated gun comprising, a fixed receiver having a spring pressed bolt reciprocable therein, a barrel threaded into the front of said receiver and having a chamber opening thereto, said bolt being movable into closing relation to said chamber and having oppositely and laterally projecting locking lugs on its forward end, interior shelves on the sides of said receiver forming supports spaced rearwardly from the forward position of said lugs, a pair of lock levers laterally swingably supported on said supports and pivotally connected at their rear ends to said receiver, keepers on the forward ends of said levers positively lockingly coacting with the rear faces of said lugs in the forward position of said bolt, spring means biasing said keepers toward said bolt, wing portions on said levers extending arcuately through the sides of said receiver for longitudinal support therefrom, fingers depending from said levers and forming cam abutments for said levers spaced laterally of said receiver, another finger depending from said bolt and forming a tappet on said bolt spaced rearwardly from said cam abutments, a gas cylinder disposed under said barrel and connected at its rear end to said receiver, means forming a gas passage from said barrel to the forward end of said cylinder, a piston in said cylinder spring biased to forward position and having a piston rod extending into said receiver, and a cam in said receiver connected to said rod, said cam having oppositely cammed surfaces coacting with said cam abutments and a central fiat surface coacting with said tappet upon rearward motion of said piston, the outer ends of said lugs being disposed at the same level as and coacting with the inner edges of said levers during retraction of said bolt to hold said levers in laterally displaced unlocked position.

2. A gas operated gun comprising a fixed receiver having a spring pressed bolt reciprocable therein, a barrel releasably engaged with the front of said receiver and having a chamber opening thereto, said bolt being movable into closing relation to said chamber and having a laterally projecting locking lug on its forward end, a support on said receiver spaced rearwardly from the forward position of said lug, s. lock lever laterally swingably supported on said support and pivotally associated at its rear end with said receiver, a keeper on the forward end of said lever positively lockingly coacting with the rear face of said lug in the forward position of said bolt, spring means biasing said keeper toward said bolt, a finger depending from said lever and forming a cam abutment on said lever, another finger depend-ing from said bolt and forming a tappet on said bolt spaced rearwardly from said cam abutment, a gas cylinder extending alongside said barrel and connected at its rear end to said receiver, means forming a gas passage from said barrel to the forward end of said cylinder, a piston in said cylinder spring biased to forward position and having a piston rod extending into said receiver, and a member in said receiver connected to said rod and having a cammed surface coacting with said cam abutment and another surface coacting with said tappet upon rearward motion of said piston, the outer end of said lug being disposed at the same level as and coacting with the inner edge of said lever during retraction of said bolt to hold said lever in laterally displaced unlocked position.

3. A gas operated gun comprising, a fixed receiver having'a spring pressed bolt of rectangular cross section reciprocable therein, said receiver having a removable cover and open top through which said bolt may be removed, a barrel releasably engaged with the front of said receiver and having a chamber opening thereto, a head portion on said bolt and movable into closing relation to said chamber and having laterally projecting locking lugs near'its forward end, interior supports on the sides of said receiver spaced rearwardly from the forward position of said lugs and forming ways for said bolt, lock levers laterally swingably supported on said supports and pivotally associated at their rear ends with said receiver, keepers on the forward ends of said levers positively lockingly coacting with the rear faces of said lugs in the forward position of said bolt, spring means biasing said keepers toward said bolt, fingers depending from said levers and forming cam abutments on said levers, another finger depending from said bolt and form ing a tappet on said bolt spaced rearwardly from said cam abutments, a gas cylinder extending alongside said barrel and connected at its rear end to said receiver, means forming a gas passage from said barrel to the forward end of said cylinder, a. piston in said cylinder spring biased to forward position and having a piston rod extending into said receiver, and a member in said receiver connected to said rod and having cammed surfaces coating with said cam abutments and another surface coacting with said tappet upon rearward motion of said piston, the outer ends of said lugs being disposed at the same level as and coacting with the inner edges of said levers during retraction of said bolt to hold said levers in laterally displaced unlocked position.

References Cited in the file of this patent UNITED STATES PATENTS 6 Penney Feb. 27, 1945 Lippert et al. Jan. 2, 1951 Lippert et a1. Apr. 1, 1952 Clarke July 1, 1952 FOREIGN PATENTS Great Britain June 22, 1939 Italy Jan. 4, 1945 Switzerland July 16, 1946 

